The State Department on Monday warned Americans traveling to Europe of an increased risk of terrorist attacks, particularly over the holiday season, NBC News reported.

"Credible information indicates the Islamic State of Iraq and the Levant (ISIL the U.S. gov't acronym for ISIS or Da'esh), al-Qaeda, and their affiliates continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events," the travel advisory read.

The State Department urged travelers to avoid large crowds and exercise caution at tourist sites, festivals, large holiday events and outdoor markets.

Terrorists have carried out attacks in Belgium, France, Germany and Turkey this year but the advisory warns of the potential for attacks throughout the continent.